Method of recovering powered aluminum from aluminum-polymer mixtures

Abstract

Solid composite propellants for rocket motors normally consist of an oxidizer and and aluminum powder cured in a polymeric binder system. The oxidizer, ammonium perchlorate, can be readily removed by suitable solvents leaving a residue consisting primarily of aluminum and polymer. The aluminum and polymer are separated by a process that is based upon the differential oxidation of the polymer leaving the aluminum in its original powder form. Aluminum metal forms, on exposure to air, an extremely tough inert aluminum oxide coating. Because of this, aluminum is extremely resistant to further oxidation even at temperatures up to its melting point at 660 DEG C. Most organic compounds, including polymers, are oxidized to carbon dioxide at much lower temperatures (400 DEG -600 DEG C.). Due to this difference in reactivity, it is possible to remove the polymer from the aluminum as carbon dioxide leaving the aluminum residue.

What is claimed is: 
     
       1. A method of recovering aluminum powder from a solid composite propellant comprising a polymeric binder and an oxidizer comprising the steps of: dissolving the composite propellant in a solvent to remove soluble polymer and the oxidizer,   drying the insoluble residue, and   heating the dried insoluble residue in an oxidizing gas to a temperature at which the polymer oxidizes but below the melting temperature of aluminum to remove the polymer by oxidation to innocuous gaseous products and to leave a residue of free flowing aluminum powder.   
     
     
       2. A method according to claim 1 in which the dried insoluble residue is heated to a temperature in the range of 400° C. to 660° C. 
     
     
       3. A method according to claim 2 in which the dried insoluble residue is heated in air. 
     
     
       4. A method according to claim 3 in which the dried insoluble residue is heated to a temperature of about 550° C. for about 4 hours.